As video game software (hereinafter, referred to as video game software) which is executed by a specialized video game machine (hereinafter, referred to as a video game machine) with an embedded computer, a personal computer, or the like, there is video game software which expresses a three-dimensional space or reproduces a motion image according to the progress of the video game. There is also a reproducer which reproduces video content recorded in a commercially available DVD (Digital Versatile Disc) video, Blu-ray (Registered Trademark) disc video, or the like (hereinafter, referred to as DVD video or the like) depending on user's operation.
A video game machine which executes video game software or a reproducer which reproduces video content is an information processor which performs information processing. In general, the information processor is connected to an amplifier including a sound emission device, such as a speaker, and transmits a sound signal to the amplifier such that sound is synchronized with video of the content. Although many information processors mix sound such that a sound field is formed in accordance with the standard audio environment defined in advance over all contents and then transmit the sound to the amplifier, an information processor which changes a sense of sound field in accordance with the progress of a content to obtain a sense of reality or a sense of strong impact has been developed. For example, Patent Literature 1 discloses a technique which switches the effects of reproduced sound in accordance with the progress of a video game.